JPH11242165A - Real-image finder optical system and device using the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the finder magnification by giving a power to the reflection face of an image inverting optical system on the observer side of an intermediate image. SOLUTION: An objective optical system Ob has plural lens groups G1 to G3 and is so constituted that intervals between plural lens groups are changed at the time of varying the magnification from the wide angle end to the telephoto end, and an image inverting optical system PP has plural reflection faces, and at least one reflection face arranged on the side of an eyepiece optical system Oc of an object image out of these reflection faces is formed to a curved reflection face which gives a power to a luminous flux, and the image inverting optical system PP is provided with an asymmetrical surface of revolution which corrects asymmetric decentration aberration of revolution caused by the curved reflection face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type viewfinder optical system and an apparatus using the same, and is particularly suitable for a still camera, a still video, etc. in which a photographing optical system and a viewfinder optical system are provided separately. The present invention relates to a real image type finder optical system having an image inversion optical system and an apparatus using the same.

[0002]

2. Description of the Related Art Generally, when a photographing optical system and a finder optical system are provided separately as in a lens shutter camera or the like, the finder optical system can be roughly classified into a virtual image finder and a real image finder.

The virtual image finder has a large front lens diameter due to its configuration, and the view of the field frame is unclear, and there is a major problem in miniaturizing the finder optical system and improving its performance. On the other hand, in the case of a real image type viewfinder, place the field frame near the intermediate image plane of the objective optical system and observe the boundary line of the field frame clearly in order to observe it with the eyepiece optical system. Can be. Further, since the entrance pupil position is close to the object side, the size of the objective optical system can be reduced in the radial direction, and most of the lens shutter cameras that claim small size and high performance employ a real image type viewfinder.

Recently, in order to further reduce the size of a real image type finder, a method of reducing the focal length of an objective optical system while maintaining a required angle of view, that is, reducing the image height of an intermediate image. Is often used. As a result, the ratio of the focal lengths of the objective optical system and the eyepiece optical system, that is, the so-called finder magnification, is sacrificed at present. For that reason, although it claims small size and high performance,
The image actually observed is very small and hard to see.

[0005] Simply reducing the focal length of the eyepiece optical system,
If various aberrations generated can be corrected, it is possible to enlarge the observed image. However, even if aberration correction is possible, there is a limit to reducing the focal length of the eyepiece optical system because it is necessary to secure the optical path length of the image inversion optical system. In general, the eyepiece optical system is often a single lens, and when the focal length is reduced, chromatic aberration particularly deteriorates.
There is also a problem that the correction cannot be performed.

In view of the above, recently, there have been some proposals to configure a reflecting surface of an image inverting optical system of a real image type finder, that is, a reflecting surface or a mirror of a prism constituting the image inverting optical system with a curved surface to have power. I have. However, the reflection surface of the image inversion optical system is generally decentered with respect to the optical axis, and when the surface is given power, rotationally asymmetric eccentric aberration occurs. The eccentric aberration cannot be corrected in principle only by a rotationally symmetric surface.

[0007] In the case of the conventional Japanese Patent Laid-Open No. 8-248481,
A rotationally symmetric curved surface is used for the reflecting surface of the prism of the real image type zoom finder of the lens shutter camera. Although it is described that the curved surface can be an aspheric surface or a toric surface, the aspheric surface disclosed in the specification is rotationally symmetric, and the toric surface is also symmetric with respect to two coordinate axes. Correction for skew rays is not sufficient. Further, in each of the examples, the reflecting surface of the prism is a curved surface, but the prism is disposed on the object side of the intermediate image, and there is no intention to reduce the focal length of the eyepiece optical system.

Japanese Patent Application Laid-Open No. 9-152646 uses a rotationally asymmetric curved surface as a reflecting surface of a prism of a real image finder of a lens shutter camera for a single focus lens. As described in the specification, the prism is disposed closer to the object side than the intermediate image to serve as an objective lens, and there is no intention to reduce the focal length of the eyepiece optical system. Also, EP0722106A2,
JP-A-8-248481 and JP-A-9-15264
It is exactly the same as the contents of No. 6.

Further, JP-A-8-292368, JP-A-8-292371, JP-A-8-292372, JP-A-9-5650, JP-A-9-90229, JP-A-9-212330, JP-A-9-212330 JP-A-212331, JP-A-9-222561, JP-A-9-258105, and JP-A-9-258106 disclose images using a prism optical system using a rotationally asymmetric surface in a single focus and zoom image pickup apparatus. This is an example in which inversion is performed. Some examples are described as being applicable to the viewfinder optical system, but none of them relate to the real image type viewfinder.Moreover, the power of the prism reflecting surface of the eyepiece optical system is given, and the optical path length of the image inversion optical system is maintained. There is no intention to reduce the focal length as it is.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation of the prior art, and an object of the present invention is to convert an intermediate image formed by an objective optical system into an erect image formed by an image inverting optical system. Provides a real-image finder optical system that increases the finder magnification by giving power to the reflection surface of the image reversing optical system on the observer's side rather than the intermediate image in the real-image finder optical system that observes through the eyepiece optical system It is to be.

Another object of the present invention is to provide a real image type finder optical system in which chromatic aberration is reduced by giving power to a reflecting surface of an image inverting optical system free from chromatic aberration.

It is a third object of the present invention to provide a real image type finder optical system in which the number of assembly steps, accuracy and cost are reduced by simplifying the configuration.

It is a fourth object of the present invention to provide a real image type finder optical system having a field frame without coloring.

A fifth object is to provide a real image type finder optical system having a rotationally asymmetric surface which is easy to manufacture.

[0015]

According to the present invention, there is provided a real-image finder optical system which achieves the above object, and an image for converting an object image formed by the finder objective optical system into an erect image. In a real image type finder optical system including a reversing optical system and an eyepiece optical system, and forming a finder optical path separated from a photographing optical path, the finder objective optical system has a plurality of lens groups and has a wide-angle end. Upon zooming from to the telephoto end, it is configured to change the group spacing of the plurality of lens groups, the image inversion optical system has a plurality of reflection surfaces, among the plurality of reflection surfaces,
The shape of at least one reflection surface disposed closer to the eyepiece optical system than the object image is formed by a curved reflection surface that gives power to a light beam, and the image inversion optical system is generated by the curved reflection surface. It is characterized by having a rotationally asymmetric surface for correcting rotationally asymmetric eccentric aberration.

In this case, the following conditions (3-1) and (3)
It is desirable to satisfy -2). 0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) where PXn and PYn are the main axes of the reflecting surfaces each having power. The power of the surface in the X and Y directions near the ray,
PX and PY pass parallel rays of a small height Δ in the X and Y directions along the axial principal ray from the intermediate image toward the observer side, and the rays are transmitted to the observer side. This is a value obtained by dividing the sine of the inclination angle with respect to the axial principal ray emitted from the nearest plane by the above Δ, and is a value defined as the power in the X and Y directions of the entire eyepiece optical system.

Another real-image finder optical system according to the present invention comprises an objective optical system for a finder, an image inverting optical system for converting an object image formed by the objective optical system for a finder into an erect image, and an eyepiece optical system. In a real image type finder optical system that forms a finder optical path separated from a photographing optical path, the image inverting optical system has a plurality of reflection surfaces, and the object image is included in the plurality of reflection surfaces. The shape of at least one reflecting surface disposed closer to the eyepiece optical system is formed by a curved reflecting surface that gives power to a light beam, and the image inverting optical system has a rotationally asymmetric shape generated by the curved reflecting surface. A rotationally asymmetric surface for correcting eccentric aberration is provided, and the following conditions (3-1) and (3-
2) is satisfied. 0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) where PXn and PYn are the main axes of the reflecting surfaces each having power. The power of the surface in the X and Y directions near the ray,
PX and PY pass parallel rays of a small height Δ in the X and Y directions along the axial principal ray from the intermediate image toward the observer side, and the rays are transmitted to the observer side. This is a value obtained by dividing the sine of the inclination angle with respect to the axial principal ray emitted from the nearest plane by the above Δ, and is a value defined as the power in the X and Y directions of the entire eyepiece optical system.

Hereinafter, the reason and operation of the above-described configuration in the present invention will be described. In the real image type finder, an image inverting optical system is used between the objective optical system and the eyepiece optical system to make an erect erect image in order to observe an intermediate image (inverted real image) formed by the objective optical system through the eyepiece optical system. There is a need. Therefore, the configuration of the objective optical system and the focal length of the eyepiece optical system are limited by the position of the intermediate image with respect to the image inverting optical system, the refractive index of the optical member of the image inverting optical system, and the way of reflection.
In particular, when the position of the intermediate image is located closer to the objective optical system side, it is necessary to secure the optical path length of the image inverting optical system, so that the focal length of the eyepiece optical system cannot be made sufficiently small, and the finder magnification increases. It is difficult to make it sufficiently large. This is because the principal point position of the eyepiece optical system is restricted by being located closer to the observer than the image inversion optical system. Therefore, if the principal point of the eyepiece optical system can be moved inside the image inversion optical system, the focal length of the eyepiece optical system should be reduced while maintaining the optical path length of the image inversion optical system that only performs image inversion. And a large image can be observed.

Generally, in order to move the principal point of the eyepiece optical system into the image inverting optical system, it is easily considered that the eyepiece optical system is composed of a plurality of lenses having different signs. However, it is difficult to construct with multiple lenses in terms of cost,
Even if that is possible, in order to sufficiently move the principal point of the eyepiece optical system inside the image inversion optical system, it is necessary to increase the power of each of the lenses with different signs and keep the lens spacing to some extent. is there. Therefore, the thickness of the eyepiece optical system is increased, which is contrary to miniaturization.

Therefore, in the present invention, the above-described configuration is adopted by focusing on the reflection surface inside the image inversion optical system, not on the eyepiece optical system itself. In other words, the image inversion optical system has a reflection surface for performing image inversion therein, and by giving power to the reflection surface, the principal point position of the eyepiece optical system is moved into the image inversion optical system. It is possible to do. This also corresponds to causing the image inversion optical system to share part of the power of the eyepiece optical system. In other words, by combining the image inverting optical system on the observer side with respect to the intermediate image and the existing eyepiece optical system so as to have an action as one eyepiece optical system, the optical path length required for image inversion is reduced. The main point position of the eyepiece optical system is moved into the image inversion optical system while the distance is maintained, so that the focal length can be reduced.

Generally, the reflecting surface of the image inversion optical system is
Tilt to fold the light path. Therefore, the coordinate system will be described first. Passing through the center of the object point, reaching the center of the intermediate image plane through the center of the aperture or the center of the aperture of the objective optical system,
Further, a ray passing through the eyepiece optical system and entering the center of the pupil is defined as an axial principal ray. Next, the optical axis defined by a straight line that intersects the first surface of the optical system is defined as a Z-axis. It is defined as a Y axis, and an axis orthogonal to the optical axis and orthogonal to the Y axis is an X axis. The ray tracing direction is forward ray tracing from the object to the image plane.

Next, the rotationally asymmetric surface used in the present invention will be described. Generally, in a spherical lens system composed only of spherical lenses, spherical aberration generated by a spherical surface, coma aberration, field curvature and other aberrations are mutually corrected on several surfaces, so that the overall aberration is reduced. Has become.

On the other hand, in order to favorably correct aberrations with a small number of surfaces, a rotationally symmetric aspherical surface or the like is used. This is to reduce various aberrations generated on the spherical surface. When a rotationally symmetric optical system is decentered, rotationally asymmetric aberrations occur, and it is in principle impossible to correct this only with a rotationally symmetric optical system. The rotationally asymmetric aberrations caused by this eccentricity include distortion, field curvature, astigmatism and coma which also occur on the axis. In the present invention, in order to correct the rotationally asymmetric aberration generated due to the eccentricity, a rotationally asymmetric surface is arranged in the image inversion optical system to correct the rotationally asymmetric aberration.

Rotationally asymmetric aberrations generated by a decentered concave mirror include rotationally asymmetric field curvature. For example, a ray incident on a concave mirror decentered from an object point at infinity is reflected and imaged by the concave mirror.After the ray hits the concave mirror, the rear focal length to the image plane is Becomes half of the radius of curvature of the part hit by. Then, as shown in FIG. 13, an image plane inclined with respect to the axial principal ray is formed. It is impossible to correct such rotationally asymmetric curvature of field with a rotationally symmetric optical system. In order to correct the tilted curvature of field, the concave mirror M is constituted by a rotationally asymmetric surface. Can be corrected by weakening the curvature (reducing the refractive power). Further, by arranging a rotationally asymmetric surface having the same effect as the above configuration in the optical system separately from the concave mirror M, a flat image surface can be obtained with a small number of components.

Next, rotationally asymmetric astigmatism will be described. As described above, the eccentrically arranged concave mirror M
In this case, astigmatism as shown in FIG. 14 also occurs for axial rays. This astigmatism can be corrected by appropriately changing the curvature in the X-axis direction and the curvature in the Y-axis direction of the rotationally asymmetric surface, as described above.

Further, rotationally asymmetric coma will be described. Similarly to the above description, in the concave mirror M arranged eccentrically, coma as shown in FIG. To correct the coma aberration, the inclination of the surface can be changed as the distance from the origin of the X axis of the rotationally asymmetric surface increases, and the inclination of the surface can be appropriately changed depending on the sign of the Y axis.

The reflecting surface of the image reversing optical system having power as in the present invention is tilted with respect to the axial principal ray for performing image reversal, where rotationally asymmetric decentering aberration occurs. . When the power itself is small, the rotationally asymmetrical eccentric aberration that occurs is small and can be tolerated sufficiently. However, it is impossible in principle to correct it sufficiently with a rotationally symmetric lens.

Therefore, in the present invention, by introducing a rotationally asymmetric surface into the image inverting optical system, it becomes possible to sufficiently correct rotationally asymmetric decentering aberration. As a result, an increase in the finder magnification, which is the object of the present invention, is achieved.

It is desirable to use a rotationally asymmetric surface as a reflection surface of an image inversion optical system. This is because the reflecting surface of the image inversion optical system is inclined with respect to the axial chief ray, so even the surface with small rotational asymmetry can efficiently correct the eccentric aberration that occurs on the reflecting surface with power. Because you can. In addition, the correction effect is higher when it is arranged on the reflection surface than when it is arranged on the transmission surface of the image inversion optical system.

When power is given to the reflecting surface, no chromatic aberration occurs in principle on that surface. Therefore, even if the eyepiece optical system is composed of a single lens or only an image inverting optical system having power, and the focal length of the eyepiece optical system is reduced, as in the present invention, the eyepiece optical system is In this case, a real image type finder with a small occurrence of chromatic aberration, which is the object of the present invention, can be obtained by employing a configuration in which the power of (1) is shared by the reflection surface of the image inversion optical system. In particular, if the reflecting surface of the image reversing optical system on the observer side with respect to the intermediate image surface is given power for the purpose of increasing the finder magnification, a field frame without coloring is observed, which is preferable.

Preferably, the rotationally asymmetric surface is located closer to the eyepiece optical system than the object image. This is because it is desirable in terms of eccentric aberration correction to dispose a rotationally asymmetric surface for eccentric aberration correction at a position close to the curved reflecting surface where eccentric aberration occurs.

When the rotationally asymmetric surface used in the present invention is applied particularly to a refracting surface, it is desirable that the surface be decentered with respect to the axial ray. With such a configuration, it is possible to efficiently correct rotationally asymmetric eccentric aberration. If the rotationally asymmetric surface introduced to correct rotationally asymmetric eccentric aberration is not decentered with respect to the axial chief ray, the degree of rotational asymmetry of the rotationally asymmetric surface becomes too strong, and the sensitivity to aberrations also increases. In addition, manufacturing becomes difficult.

Also, it is decentered with respect to the axial chief ray, and
The surface having the power itself may be constituted by a rotationally asymmetric surface. This makes it possible to configure a surface with less rotationally asymmetrical eccentric aberration, even though its own surface is decentered and has power.

A plurality of rotationally asymmetric surfaces may be arranged in the image reflecting optical system. Providing a plurality of lenses increases the degree of freedom in design, and allows the correction of aberrations to be shared between the respective surfaces, thereby achieving good correction.

It is also possible to give power to the image inversion optical system and integrate it with the eyepiece optical system. This eliminates the components of the current eyepiece optical system, and is advantageous in terms of cost, assembling man-hours, and accuracy.

It is preferable that the rotationally asymmetric surface applied to the real image type viewfinder of the present invention has no rotationally symmetric axis both inside and outside the surface. In the case of having a rotationally symmetric axis in the plane and out of the plane, for example, a toric surface off the rotationally symmetric axis, a parabolic surface, etc. Since a symmetric component remains, it is impossible to sufficiently correct rotationally asymmetric eccentric aberration.

Here, as an example, a rotationally asymmetric surface (hereinafter, referred to as a free-form surface) is considered as defined by the following equation. _{Z = C 2 + C 3 y} + C 4 x + C 5 y 2 + C 6 yx + C 7 x 2 + C 8 y 3 + C 9 y 2 x + C 10 yx 2 + C 11 x 3 + C 12 y 4 + C 13 y 3 x + C 14 y 2 x 2 + C ^{_{15 yx 3 + C 16 x 4}} + C 17 y 5 + C 18 y 4 x + C 19 y 3 x 2 + C 20 y 2 x 3 + C 21 yx 4 + C 22 x 5 + C 23 y 6 + C 24 y 5 x + C 25 y 4 x 2 + C ^{_{26 y 3 x 3 + C 27}} y 2 x 4 + C 28 yx 5 + C 29 x 6 + C 30 y 7 + C 31 y 6 x + C 32 y 5 x 2 + C 33 y 4 x 3 + C 34 y 3 x 4 + C 35 y 2 ^{_{x 5 + C 36 yx 6 +}} C 37 x 7 ····· ··· (a) provided that, C _m (m is an integer of 2 or more) is a coefficient.

The free-form surface generally includes an XZ plane,
Although neither YZ plane has a plane of symmetry, in the present invention, x
By setting all the odd-order terms to 0, a free-form surface having only one symmetry plane parallel to the YZ plane is obtained. For example, in the above definition formula (a), C ₄ , C ₆ , C ₉ ,
_{C 11, C 13, C 15} , C 18, C 20, C 22, C 24, C 26, C
_{28, C 31, C 33,} C 35, C 37, 0 the coefficients of each term of ...
Is possible.

By setting all the odd-order terms of y to 0, a free-form surface having only one symmetry plane parallel to the XZ plane is obtained. For example, in the definition formula (a),
C ₃ , C ₆ , C ₈ , C ₁₀ , C ₁₃ , C ₁₅ , C ₁₇ , C ₁₉ , C
_{21, C 24, C 26,} C 28, C 30, C 32, C 34, C 36, ··
It is possible by setting the coefficient of each term of 0 to 0, and it is possible to improve the manufacturability by having the above-mentioned plane of symmetry.

More preferably, if there is no plane of symmetry, the degree of freedom increases correspondingly, and it goes without saying that it is advantageous for aberration correction.

Further, the above-mentioned definition expression (a) is shown as one example as described above, and the feature of the present invention is to correct rotationally asymmetric aberration generated by eccentricity on a rotationally asymmetric surface. Therefore, it goes without saying that the same effect can be obtained for any other definition expression expressing a rotationally asymmetric surface.

As another definition of a free-form surface, Zer
It can be defined by a nike polynomial. The shape of this surface is defined by the following equation (b). The Z axis of the definition formula is Zer
This is the axis of the Nike polynomial. The definition of a rotationally asymmetric surface is X
-Defined in polar coordinates of the height of the Z axis with respect to the Y plane, A is the distance from the Z axis in the XY plane, R is the azimuth around the Z axis, and can be represented by the rotation angle measured from the Z axis .

X = R × cos (A) Y = R × sin (A) Z = D ₂ + D ₃ R cos (A) + D ₄ R sin (A) + D ₅ R ² cos (2A) + D ₆ (R ² −1 ^{_{) + D 7 R 2 sin (}} 2A) + D 8 R 3 cos (3A) + D 9 (3R 3 -2R) cos (A) + D 10 (3R 3 -2R) sin (A) + D 11 R 3 sin (3A) + D ^{_{12 R 4 cos (4A) +}} D 13 (4R 4 -3R 2) cos (2A) + D 14 (6R 4 -6R 2 +1) + D 15 (4R 4 -3R 2) sin (2A) + D 16 R 4 sin (4A ^{_{) + D 17 R 5 cos (}} 5A) + D 18 (5R 5 -4R 3) cos (3A) + D 19 (10R 5 -12R 3 + 3R) cos (A) + D 20 (10R 5 -12R 3 + 3R) sin (A) ^{_{+ D 21 (5R 5 -4R 3}} ) sin (3A) + D 22 R 5 sin (5A) + D 23 R 6 cos (6A) + D 24 (6R 6 -5R 4) cos (4A) + D 25 (15R 6 -20R 4 ^{+ 6R 2) cos (2A)} + D 26 (20R 6 -30R 4 + 12R 2 -1) + D 27 (15R 6 -20R 4 + 6R 2) sin (2A) ^{_{D 28 (6R 6 -5R 4)}} sin (4A) + D 29 R 6 sin (6A) ····· ··· (b) In addition, to design an optical system symmetric with respect to the X direction,
_{D 4, D 5, D 6} , D 10, D 11, D 12, D 13, D 14, D
₂₀ , D ₂₁ , D ₂₂ ... May be used.

As an example of other aspects, the following definition formula is given. _{Z = Σ n Σ m C nm} x n y nm However, sigma _n is sigma
The n is 0 to k, sigma _m represents the m of sigma is 0 to n.

As an example, if k = 7 (seventh order),
When expanded, it can be represented by the following equation (c).

Z = C ₂ + C ₃ Y + C ₄ | X | + C ₅ Y ² + C ₆ Y | X | + C ₇ X ² + C ₈ Y ³ + C ₉ Y ² | X | + C ₁₀ YX ² + C ₁₁ | X ³ | + C ₁₂ Y ⁴ + C ₁₃ Y ³ | X | + C ₁₄ Y ² X ² + C ₁₅ Y | X ³ | + C ₁₆ X ⁴ + C ₁₇ Y ⁵ + C ₁₈ Y ⁴ | X | + C ₁₉ Y ³ X ² + C ₂₀ Y ² | X ^{_{3 | + C 21 YX 4 +}} C 22 | X 5 | + C 23 Y 6 + C 24 Y 5 | X | + C 25 Y 4 X 2 + C 26 Y 3 | X 3 | + C 27 Y 2 X 4 + C 28 Y | X 5 | ^{_{+ C 29 X 6 + C 30}} Y 7 + C 31 Y 6 | X | + C 32 Y 5 X 2 + C 33 Y 4 | X 3 | + C 34 Y 3 X 4 + C 35 Y 2 | X 5 | + C 36 YX 6 + C 37 | X ⁷ | (c) In addition, both the powered reflecting surface and the rotationally asymmetric surface in the image inversion optical system applied to the present invention are arranged on the surface closer to the observer than the intermediate image surface. Is preferred. If the objective optical system is closer to the objective optical system than the intermediate image plane, there is no contribution to the principal point position of the eyepiece optical system, and the focal length of the eyepiece optical system cannot be reduced. At the same time, if neither the rotationally asymmetric surface nor the reflecting surface with the power is closer to the observer than the intermediate image surface, rotationally asymmetric eccentric aberration remains in the final observation image, and the correction cannot be performed.

Further, if a plurality of reflecting surfaces with power used in the present invention are used, the degree of freedom of aberration correction increases accordingly.
Needless to say, it is preferable. The objective optical system used in the present invention can be applied to a zoom lens and a single focus lens.

It is desirable that the following conditional expression is satisfied. The following conditional expression relates to, for example, a bow-shaped rotationally asymmetric image distortion that curves like a bow when a horizontal line is captured. As shown in FIG. 16, when the objective optical system is a single focus lens, the main ray having the maximum angle of view in the X direction in the YZ plane at the wide-angle end is in the state when the objective optical system is a single focus lens and the rotationally asymmetric surface. When the difference between the tan value of the normal line of the rotationally asymmetric surface at the intersection and the tan value of the normal line of the rotationally asymmetric surface at the point where the axial principal ray intersects the rotationally asymmetric surface is DY. , | DY | <0.5 (1-1) It is important to satisfy the following condition. If the upper limit of 0.5 to the above conditional expression is exceeded, bow-shaped image distortion will be overcorrected, and the image will be bowed.

More preferably, it is preferable to satisfy the following condition: | DY | <0.3 (1-2)

The following conditional expression relates to image distortion occurring in a trapezoid. Set the eccentric direction of the rotationally asymmetric surface to Y-
When the objective optical system is a single focus lens, the main ray having the maximum angle of view in the Y positive direction at the wide angle end and the maximum image in the Y negative direction at the wide angle end are assumed to be in the Z plane. When the ratio of the curvature in the X direction of the portion where the principal ray of the angle collides with the surface is Cxn (R), | Cxn (R) | <1 (2-1) or 1 <| Cxn ( R) | <10 (2-2) It is important to satisfy one of the following conditions. When the value exceeds the range of the above conditional expression, when light rays in the positive Y direction are reflected, the trapezoidal distortion in which the upper side is shortened in the negative Y direction becomes too large, and it becomes impossible to correct on other surfaces. . On the other hand, when the light reflected in the negative Y direction is reflected, a large trapezoidal distortion in which the upper side is shortened in the positive Y direction is generated, and it is difficult to perform correction on another surface.

When | Cxn (R) | becomes 1, the trapezoidal distortion generated on this surface cannot be reduced, so that the trapezoidal distortion is generated. That is, 1
It is important to balance each other with values that fall under conditions other than those described above.

More preferably, 0.5 <| Cxn (R) | <1 (2-3) or 1 <| Cxn (R) | <3 (2-4) Is preferably satisfied.

The following condition relates to the power of the rotationally asymmetric surface. Now, when passing a parallel light beam having a small height Δ in the X direction and the Y direction along the axial principal ray from the intermediate image formed by the objective optical system toward the observer, The value obtained by dividing the sine of the tilt angle with respect to the axial principal ray emitted from the plane closest to the observer side by the above Δ is defined as the power in the X direction and the Y direction of the entire eyepiece optical system. I do.

Next, the powers of the surfaces in the X and Y directions near the axial principal ray of the reflecting surface to which the power is applied are respectively expressed by PX
n and PYn. At that time, it is important to satisfy the following conditions.

0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) These conditional expressions define the power of the reflecting surface. This is a conditional expression provided to reduce chromatic aberration generated in the eyepiece optical system and to effectively correct rotationally asymmetric aberration. If the upper limits of these conditional expressions are exceeded, the power of the rotationally asymmetric surface becomes too strong, and rotationally asymmetric aberrations generated on the rotationally asymmetric surface are overcorrected. As a result, the correction cannot be performed on other surfaces. At the same time, in order to obtain the desired power of the entire eyepiece optical system, chromatic aberration generated on the refracting surface is adversely affected, which makes it difficult to balance rotationally asymmetric aberration correction.

More preferably, 0 <| PXn / PX | <3 (3-1 ′) 0 <| PYn / PY | <3 (3-2 ′) This is advantageous in terms of correction and surface fabrication.

More preferably, it is desirable to satisfy the following condition: 0 <| PXn / PX | <1 (3-1 ") 0 <| PYn / PY | <1 (3-2")

More preferably, 0 <| PXn / PX | <0.7 (3-1 ″ ′) 0 <| PYn / PY | <0.7 (3-2 ″ ′) It is desirable to be satisfied.

In the present invention, it is desirable to satisfy the following conditional expressions. 0.1 <1 / | PX × d / n | <1 (4-1) 0.1 <1 / | PY × d / n | <1 (4-2) where d Is the length of the axial principal ray when the image inversion optical system on the observer side with respect to the intermediate image is developed, and n is the refractive index of the image inversion optical system on the observer side with respect to the intermediate image. If the lower limit of these conditional expressions is exceeded, not only the power as the eyepiece optical system becomes too strong to perform aberration correction, but also the principal point position of the eyepiece optical system enters the image inversion optical system too much, and image inversion is performed. In such a case, the image inversion optical system becomes too large. If the upper limit is exceeded, the principal point position of the eyepiece optical system cannot be largely moved into the image inverting optical system, and the focal length of the eyepiece optical system cannot be reduced.

More preferably, 0.3 <1 / | PX × d / n | <1 (4-1 ′) 0.3 <1 / | PY × d / n | <1 (4) Satisfying 4-2 ′) is preferable because a real image finder excellent in aberration correction can be obtained.

More preferably, 0.5 <1 / | PX × d / n | <1 (4-1 ′) 0.5 <1 / | PY × d / n | <1 (1) 4-2 ′) is desirably satisfied.

More preferably, 0.6 <1 / | PX × d / n | <1 (4-1 ″) 0.6 <1 / | PY × d / n | <1 (1) 4-2 ”) is desirably satisfied.

In the present invention, it is desirable to satisfy the following conditional expressions. 0.03 <PX <0.5 (5-1) 0.03 <PY <0.5 (5-2) These conditional expressions define the focal length of the eyepiece optical system. is there. If these lower limits are exceeded, the focal length of the eyepiece optical system becomes too large, and it becomes impossible to increase the finder magnification.

More preferably, it is desirable to satisfy 0.04 <PX <0.3 (5-1 ') 0.04 <PY <0.3 (5-2')

More preferably, it is desirable to satisfy the following condition: 0.05 <PX <0.1 (5-1 ") 0.05 <PY <0.1 (5-2")

[0066]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a real image type finder optical system and an apparatus using the same according to the present invention will be described below. FIG. 1 shows a YZ cross-sectional view (a) and an XZ cross-sectional view (b) of the real image finder according to the first embodiment at the wide-angle end. First, when describing the coordinate system, as a distant object point center, to reach the intermediate image plane S ₁₁ centered through the opening center of the objective optical system Ob, further enters the ocular optical system Oc as the exit pupil center A light ray is defined as an axial principal ray, an optical axis defined by a straight line until the axial principal ray intersects the first surface S ₁ of the optical system is defined as a Z axis, and the real image finder is orthogonal to the Z axis. The axis within the eccentric plane of each free-form surface to be formed is defined as the Y axis, and the axis orthogonal to the Z axis and orthogonal to the Y axis is defined as the X axis.

In the first embodiment, as shown in FIG. 1, in order from the object side, an objective optical system Ob having a positive refractive power and a porro prism capable of reducing the thickness (Z-axis direction) as an image inverting optical member are used. This is a real image type finder including an image reversal optical system PP and an eyepiece optical system Oc having a positive refractive power.
Reference numerals S _{1 to} S ₁₈ are given to the surfaces constituting the optical system in order from the object side. The intermediate image plane is S ₁₁ and the eye point is S ₁₈ .

More specifically, the objective optical system Ob includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, and a third group G3 having a negative refractive power. Is a zoom lens having a zoom ratio of about 3 times, which changes the magnification by changing the distance between the respective groups. The third surface S ₃ , the fourth surface S ₄ , and the fifth surface S
₅ , a rotationally symmetric aspheric surface given by the following equation (d) is used. When at least a part P1 of the image inverting optical system is arranged between the objective optical system Ob and the intermediate image, the use of such a negative-group-leading zoom lens ensures an optical path length, and thus is a preferable configuration. .

A Porro prism is used as the image reversing optical system PP, each of which has two reflecting surfaces S ₈ and S ₈ .
_9, it consists of S _13, 2 two blocks with S ₁₄ P1, P2, during which the intermediate image plane S ₁₁ intermediate image of the object by the objective optical system Ob is formed. In this embodiment, a rotationally asymmetric surface given by the following equation (a) is applied to the two reflecting surfaces S ₁₃ and S ₁₄ of the block P2 on the viewer side of the intermediate image in the Porro prism. And the refraction surface S on the incident side
₁₂ also has a curvature. At the same time, with the curvature on the refractive surface S ₇ on the entrance side of the block P1 on the object side, has introduced a rotationally symmetric aspherical surface there is given by the following formula (d). Also, the eyepiece optical system Oc is composed of one positive lens,
Have introduced a rotationally symmetric aspheric the surface S ₁₆ on the object side is given by the following formula (d).

With such a configuration, power is provided inside the Porro prism disposed between the intermediate image and the eyepiece optical system Oc. The principal point of the eyepiece optical system Oc can be moved inside the Porro prism, and the focal length of the eyepiece optical system Oc can be reduced.

The rotationally symmetric aspherical surface of this embodiment is expressed as follows: Z = (y ² / R) / [1+ {1− (1 + K) y ² / R ² } ^1/2 ] Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ + · ... (D). Here, Z is an optical axis (on-axis principal ray) where the traveling direction of light is positive, and y is a direction perpendicular to the optical axis.
Where R is the paraxial radius of curvature, K is the conic coefficient, A, B,
C, D... Are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively. Note that the Z axis in this definition expression is the axis of the rotationally symmetric aspherical surface.

The rotationally asymmetric surface of this embodiment is as follows: Z = C ₂ + C ₃ y + C ₄ x + C ₅ y ² + C ₆ xx + C ₇ x ² + C ₈ y ³ + C ₉ y ² x + C ₁₀ xx ² + C ₁₁ x ³ + C _{12 ^{y 4 + C 13 y 3 x}} + C 14 y 2 x 2 + C 15 yx 3 + C 16 x 4 + C 17 y 5 + C 18 y 4 x + C 19 y 3 x 2 + C 20 y 2 x 3 + C 21 yx 4 + C 22 x 5 + C 23 ^{_{y 6 + C 24 y 5 x}} + C 25 y 4 x 2 + C 26 y 3 x 3 + C 27 y 2 x 4 + C 28 yx 5 + C 29 x 6 + C 30 y 7 + C 31 y 6 x + C 32 y 5 x 2 + C 33 y 4 given by ^{_{x 3 + C 34 y 3 x}} 4 + C 35 y 2 x 5 + C 36 yx 6 + C 37 x 7 ····· ··· (a). The Z axis of this definition expression is the axis of the rotationally asymmetric surface.

The zoom lens constituting the objective optical system Ob will be described in detail. FIG. 2 shows each group of the objective optical system Ob according to the first embodiment at the wide-angle end (a), the standard state (b), and the telephoto end (c). is shown with respect to the refracting surface S ₇ on the incident side of the image-inverting optical system PP the position of G1 to G3. The first group G1 includes a biconcave negative lens, the second group G2 includes a biconvex positive lens, and the third group G3 includes a negative meniscus lens convex to the object side. From the wide-angle end to the telephoto end, the first lens unit G1 slightly retreats to the observation side from the wide-angle end to the standard state, is extended toward the object side from the standard state to the telephoto end, and is at the same position as the wide-angle end at the telephoto end. ,
The second group G2 and the third group G3 are extended from the observation side to the object side, but the speed of the second group G2 is higher.

The real image type viewfinder of the first embodiment has a horizontal half angle of view of 22.258 to 15.043 to 9.240 °,
Vertical half angle of view 12.586-8.542-5.274 °,
The pupil diameter is 4 mm. The constituent parameters of this embodiment will be described later. Among the constituent parameters, the plane with eccentricity is defined by the distance from the front surface along the axial principal ray emitted from the front surface. The position given by the interval is the origin, the direction in which the principal ray on the axis travels from the origin is the new Z-axis, and the direction orthogonal to the new Z-axis in the YZ section is a new Y-axis. A direction orthogonal to the new Z axis in the XZ section is defined as a new X axis. Then, a new eccentric amount (x, y, z) in the X-axis direction, Y-axis direction, and Z-axis direction with respect to the origin, and the center axis of the surface (for the free-form surface, the Z-axis For a rotationally symmetric aspherical surface, the new X-axis and Y of the Z-axis of the equation (d).)
The tilt angles (°) (α, β, γ, respectively) about the axis and the Z axis are given. In this case, α
The positive of β and β means counterclockwise with respect to the positive direction of each axis, and the positive of γ means clockwise with respect to the positive direction of Z axis. In addition, the paraxial radius of curvature of the spherical surface, the (rotationally symmetric) aspheric surface, the surface interval (the sign is inverted after reflection), the refractive index of the medium, and the Abbe number are given according to the conventional method. Also,
In the configuration parameters to be described later, a term relating to an aspheric surface for which no data is described is zero. The refractive index for d-line (wavelength 587.56 nm) is shown. The unit of the length is mm, but of course it may be multiplied by any coefficient. The same applies to the second and subsequent embodiments.

The objective optical system Ob as in this embodiment preferably satisfies one or both of the following conditional expressions. −4.0 <f ₁ / f _W <0 (6-1) 0 <| dz2 / dz1 | <2.0 (6-2) where f ₁ is the first group G1. focal length, f _W is the objective optical system Ob focal length of the entire system at the wide angle end for forming an intermediate image, dz1 change group spacing to the telephoto end from the wide angle end in the first lens group G1 and the second lens group G2 The amount dz2 is the amount of change in the group interval from the wide-angle end to the telephoto end of the second group G2 and the third group G3.

Conditional expression (6-1) is a conditional expression for sufficiently obtaining a back focus while keeping the rotationally symmetric negative distortion, which is remarkable at the wide-angle end of the objective optical system, small. If the lower limit of -0.4 is exceeded, the back focus can be obtained, but the occurrence of negative distortion becomes too large, and it becomes impossible to correct it on other surfaces. If the upper limit of 0 is exceeded, the negative distortion itself becomes small, but sufficient back focus cannot be ensured, and at the same time, miniaturization of the objective optical system becomes difficult.

The conditional expression (6-2) is a conditional expression for achieving the miniaturization of the objective optical system while obtaining the required zoom ratio. If the upper limit of 2.0 is exceeded, the amount of movement of the first and second lens groups becomes too large with respect to the third lens group, and it is not possible to reduce the size of the objective optical system particularly at the telephoto end.

Regarding conditional expression (6-1), it is desirable to satisfy the following condition: -3.0 <f ₁ / f _W <−0.1 (6-1 ′)

More preferably, it is desirable to satisfy the following condition: -2.5 <f ₁ / f _W <−0.3 (6-1 ″).

More preferably, it is desirable to satisfy the following condition: -2.0 <f ₁ / f _W <−0.5 (6-1 ″ ′).

It is preferable that the conditional expression (6-2) satisfies the following condition: 0.1 <| dz2 / dz1 | <1.5 (6-2 ')

More preferably, it is desirable to satisfy the following condition: 0.15 <| dz2 / dz1 | <1.2 (6-2 ″)

More preferably, it is desirable to satisfy the following condition: 0.2 <| dz2 / dz1 | <1.0 (6-2 ″ ′)

FIG. 3 shows YZ at the wide-angle end (a), the standard state (b), and the telephoto end (c) of the real image type viewfinder of the second embodiment.
FIG. In the second embodiment, as shown in FIG. 3, in order from the object side, an objective optical system Ob having a positive refractive power, a roof prism P3 and a pentaprism P4 whose height (Y-axis direction) can be reduced as an image inverting optical member. Is a real image type finder including an image reversing optical system PP using a lens and an eyepiece optical system Oc having a positive refractive power. Reference numerals S _{1 to} S ₁₇ are given to the surfaces constituting the optical system in order from the object side, and the numbers of the subscripts correspond to the surface numbers of the configuration parameters described later. The intermediate image plane is S ₁₀ and the eye point is S ₁₇ .

More specifically, the objective optical system Ob includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, and a third group G3 having a positive refractive power. Is a zoom lens having a zoom ratio of about 3 times, which changes the magnification by changing the distance between the respective groups. The first surface S ₁ , the third surface S ₃ , and the fifth surface S
₅ uses a rotationally symmetric aspheric surface given by the formula sixth surface S ₆ (d). Also, eighth surface S ₈ is a roof surface of the roof prism P3. Then, the intermediate image of the object by the objective optical system Ob is formed on the intermediate image plane S ₁₀ between the roof prism P3 and the pentagonal prism P4 constituting the image-inverting optical system PP. In this embodiment, have been applied rotationally asymmetric surface given by the equation to the two reflecting surfaces S ₁₂ and S ₁₃ (a) of the pentagonal prism P4 on the observer side than the intermediate image, the incident-side and with the curvature on the refractive surface S ₁₁ of the. The eyepiece optical system Oc is composed of one positive lens, and the object-side surface S ₁₅
The rotationally symmetric aspherical surface given by the above equation (d) is introduced in FIG.

With this configuration, the pentaprism P4 disposed between the intermediate image and the eyepiece optical system Oc has power inside, so that the optical path length necessary for image inversion is secured. The principal point of the eyepiece optical system Oc can be moved inside the pentaprism P4, and the focal length of the eyepiece optical system Oc can be reduced.

The zoom lens constituting the objective optical system Ob will be described in detail. The first group G1 is a biconcave negative lens,
The second group G2 includes a positive meniscus lens convex to the object side, and the third group G3 includes a positive meniscus lens convex to the observation side. From the wide-angle end to the telephoto end, the first lens unit G1 slightly retreats to the observation side from the wide-angle end to the standard state, is extended to the object side from the standard state to the telephoto end, and is at a position retracted from the wide-angle end at the telephoto end. The second group G2 and the third group G3 are extended from the observation side to the object side, but the third group G3 has a higher speed.

The real image type viewfinder of the second embodiment has a horizontal half angle of view of 27.917 to 17.459 to 10.826.
°, vertical half angle of view 19.089 to 12.051 to 7.48
9 °, the pupil diameter is 5 mm. The objective optical system Ob of this embodiment also satisfies the conditional expressions (6-1) and (6-2).

FIG. 4 shows the YZ image of the real image type viewfinder of the third embodiment at the wide-angle end (a), the standard state (b), and the telephoto end (c).
FIG. In the third embodiment, as shown in FIG. 4, in order from the object side, an objective optical system Ob having a positive refractive power, and a roof prism P3 and a pentaprism P as image inverting optical members.
4 is a real image type finder including an image reversing optical system PP using the optical system No. 4; In this embodiment, the eyepiece optical system is integrated with the pentaprism P4 of the image inversion optical system PP.
Reference numerals S _{1 to} S ₁₅ are given to the surfaces constituting the optical system in order from the object side, and the numbers of the subscripts correspond to the surface numbers of the configuration parameters described later. The intermediate image plane is S ₁₀ and the eye point is S ₁₅ .

More specifically, the objective optical system Ob includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, and a third group G3 having a positive refractive power. Is a zoom lens having a zoom ratio of about 3 times, which changes the magnification by changing the distance between the respective groups. The first surface S ₁ , the third surface S ₃ , and the fifth surface S
₅ uses a rotationally symmetric aspheric surface given by the formula sixth surface S ₆ (d). Also, eighth surface S ₈ is a roof surface of the roof prism P3. Then, the intermediate image of the object by the objective optical system Ob is formed on the intermediate image plane S ₁₀ between the roof prism P3 and the pentagonal prism P4 constituting the image-inverting optical system PP. In this embodiment, have been applied rotationally asymmetric surface given by the equation to the two reflecting surfaces S ₁₂ and S ₁₃ (a) of the pentagonal prism P4 on the observer side than the intermediate image, the incident-side The refracting surface S ₁₁ and the refracting surface S ₁₄ on the exit side also have a curvature.

The zoom lens constituting the objective optical system Ob will be described in detail. The first group G1 is a biconcave negative lens,
The second group G2 includes a positive meniscus lens convex to the object side, and the third group G3 includes a positive meniscus lens convex to the observation side. From the wide-angle end to the telephoto end, the first lens unit G1 slightly retreats to the observation side from the wide-angle end to the standard state, is extended to the object side from the standard state to the telephoto end, and is at a position retracted from the wide-angle end at the telephoto end. The second group G2 and the third group G3 are extended from the observation side to the object side, but the third group G3 has a higher speed.

The real image type viewfinder of the third embodiment has a horizontal half angle of view of 27.917 to 17.459 to 10.826.
°, vertical half angle of view 19.089 to 12.051 to 7.48
9 °, the pupil diameter is 5 mm. The objective optical system Ob of this embodiment also satisfies the conditional expressions (6-1) and (6-2).

FIG. 5 shows a YZ sectional view (a) and an XZ sectional view (b) of the real image finder of the fourth embodiment at the wide angle end. In the fourth embodiment, as shown in FIG.
This is a real image type finder including an objective optical system Ob having a positive refractive power and an image inverting optical system PP using a Porro prism as an image inverting optical member. In this embodiment,
The eyepiece optical system is a prism block P of the image inversion optical system PP.
2 and integrated. The surfaces constituting the optical system are given reference numerals S _{1 to} S ₁₆ in order from the object side, and the numbers of the subscripts correspond to the surface numbers of the configuration parameters described later. In addition,
The intermediate image plane is S ₁₁ , and the eye point is S ₁₆ .

More specifically, the objective optical system Ob includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, and a third group G3 having a negative refractive power. A zoom lens having a zoom ratio of about three times, which changes the distance by changing the distance between the groups, and has a third surface S ₃ , a fourth surface S ₄ , and a fifth surface S
_{In FIG. 5} , a rotationally symmetric aspheric surface given by the above equation (d) is used.

A Porro prism is used as the image reversing optical system PP, each of which has two reflecting surfaces S ₈ and S ₈ .
_9, it consists of S _13, 2 two blocks with S ₁₄ P1, P2, during which the intermediate image plane S ₁₁ intermediate image of the object by the objective optical system Ob is formed. In the present embodiment, among the Porro prisms, the rotationally asymmetric surfaces given by the above equation (a) are applied to the two reflection surfaces S ₁₃ and S ₁₄ of the block P2 closer to the observer than the intermediate image. , Its refracting surface S ₁₂
To give a curvature, the put curvature to the exit side of the refracting surface S _15, introduces a rotationally symmetric aspheric surface given there by the formula (d). At the same time, the object side block P1
Of with a curvature on the refractive surface S ₇ on the incident side, it has introduced a rotationally symmetric aspheric surface given there by the formula (d).

The zoom lens constituting the objective optical system Ob will be described in detail. FIG. is shown with respect to the refracting surface S ₇ on the incident side of the image-inverting optical system PP the position of G1 to G3. The first group G1 includes a biconcave negative lens, the second group G2 includes a biconvex positive lens, and the third group G3 includes a negative meniscus lens convex to the object side. From the wide-angle end to the telephoto end, the first lens unit G1 slightly retreats to the observation side from the wide-angle end to the standard state, is extended toward the object side from the standard state to the telephoto end, and is at the same position as the wide-angle end at the telephoto end. ,
The second group G2 and the third group G3 are extended from the observation side to the object side, but the speed of the second group G2 is higher.

The real image type viewfinder of the fourth embodiment has a horizontal half angle of view of 22.258 to 15.043 to 9.240 °,
Vertical half angle of view 12.586-8.542-5.274 °,
The pupil diameter is 4 mm. Objective optical system Ob of the present embodiment
Also satisfies conditional expressions (6-1) and (6-2).

FIG. 7 shows a YZ sectional view (a) and an XZ sectional view (b) of the real image finder of the fifth embodiment at the wide angle end. In Example 5, as shown in FIG. 7, in order from the object side,
This is a real image type finder including an objective optical system Ob having a positive refractive power, an image inverting optical system PP using a Porro prism as an image inverting optical member, and an eyepiece optical system Oc having a positive refractive power. Reference numerals S _{1 to} S ₁₈ are given to the surfaces constituting the optical system in order from the object side. The intermediate image plane is S ₁₁ and the eye point is S ₁₈ .

More specifically, the objective optical system Ob includes, in order from the object side, a first group G1 having a negative refractive power, a second group G2 having a positive refractive power, and a third group G3 having a negative refractive power. A zoom lens having a zoom ratio of about three times, which changes the magnification by changing the distance between the groups, has a third surface S ₃ , a fourth surface S ₄ , and a fifth surface S
_{In FIG. 5} , a rotationally symmetric aspheric surface given by the above equation (d) is used.

A Porro prism is used as the image reversing optical system PP, each having two reflecting surfaces S ₈ and S ₈ .
_9, it consists of S _13, 2 two blocks with S ₁₄ P1, P2, during which the intermediate image plane S ₁₁ intermediate image of the object by the objective optical system Ob is formed. In the present embodiment, among the Porro prisms, the rotationally asymmetric surfaces given by the above equation (a) are applied to the two reflection surfaces S ₁₃ and S ₁₄ of the block P2 closer to the observer than the intermediate image. , Its refracting surface S ₁₂
Has a curvature. At the same time, with the curvature on the refractive surface S ₇ on the entrance side of the block P1 on the object side, it has introduced a rotationally symmetric aspheric surface given there by the formula (d). Also, the eyepiece optical system Oc consists of one positive lens, introduces a rotationally symmetric aspheric the surface S ₁₆ on the object side is given by the following formula (d). This embodiment is an example in which chromatic aberration is corrected by using a rotationally asymmetric surface.

The real image type viewfinder of the fifth embodiment has a horizontal half angle of view of 22.258 to 15.43 to 9.240 °,
Vertical half angle of view 12.586-8.542-5.274 °,
The pupil diameter is 4 mm. Objective optical system Ob of the present embodiment
Also satisfies conditional expressions (6-1) and (6-2).

It is a matter of course that each optical element is made of an inorganic material such as glass, but if it is made of an organic material, it is advantageous in terms of cost. In this case, a low moisture absorbing material such as amorphous polyolefin is used. If used, the change in performance due to the environment is small, which is preferable.

As the image inverting optical system of the present invention, it is needless to say that a Porro prism, a pentaprism, and a roof prism can be applied. Of course, a prism, a penta roof prism or the like can be applied. In particular, when a prism is used as the image inverting member, the curvature of the reflection surface can be reduced to obtain the same power as the front surface reflection because of the back surface reflection by the prism.
For this reason, the Petzval sum which particularly affects field curvature can be reduced, and a flat image surface can be obtained, which is preferable. At the same time, since the reflective surface does not cause chromatic aberration, it is preferable in performance.

The rotationally asymmetric surface used in the present invention is formed such that the substantially eccentric surface of each eccentrically arranged surface is a symmetrical surface, so that the left and right sides are symmetrical with respect to the symmetrical surface. Therefore, aberration correction and manufacturability can be greatly improved.

The following describes the structural parameters of the first to fifth embodiments. In the configuration parameters, a rotationally asymmetric surface is described as a free-form surface “FFS”. Example 1 Face Number of curvature radius interval eccentric refractive index Abbe number object surface ∞ 3000.0000 1 -19.3352 1.00 1.5842 30.5 2 8.8006 d 1 3 5.4625 2.20 1.5254 55.8 ( aspherical 1) 4 -6.9319 d ₂ (aspheric 2) 5 69.5054 1.00 1.5842 30.5 (Aspherical surface 3) 6 4.3912 d ₃ 7 7.4331 3.62 1.5254 55.8 (Aspherical surface 4) 8 ∞ -5.62 Eccentricity (1) 1.5254 55.8 9 ∞ 4.62 Eccentricity (2) 1.5254 55.8 10 ∞ 0.97 11 ∞ 0.00 (Intermediate image surface ) 12 -17.9389 4.790 1.5254 55.8 13 FFS [1] -11.29 Eccentricity (3) 1.5254 55.8 14 FFS [2] 11.06 Eccentricity (4) 1.5254 55.8 15 ∞ 0.50 16 172.3724 2.50 1.4924 57.6 (Aspherical surface 5) 17 -13.7238 18.5 18 ∞ (eye _{point) FFS [1] C 5 5.8050} × 10 -3 C 7 1.1223 × 10 -2 C 8 2.4159 × 10 -4 C 10 2.0811 × 10 -4 C 12 3.3848 × 10 -6 C 14 -1.7427 × 10 ^{_{-5 C 16 -8.3378 × 10 -6 C}} 17 2.0381 × 10 -6 C 19 -5.6187 × 10 -6 C 21 -1.5115 × 10 -6 FFS [2] C 5 3.4101 × 10 -3 C 7 6.7903 × 10 - ^{_{3 C 8 4.9242 × 10 -5 C}} 10 7.7211 × 10 -5 C 12 -2.5796 × 10 - ⁶ C ₁₄ -1.7912 × 10 ^-5 C ₁₆ -1.8411 × 10 ^-5 C ₁₇ 2.8550 × 10 ^-7 C ₁₉ -9.4696 × 10 ^-7 C ₂₁ -2.3788 × 10 ^-6 Aspheric surface 1 K -0.619092 A -0.115767 × 10 ^-2 B -0.164226 × 10 ^-3 C 0.159592 × 10 ^-4 D -0.334236 × 10 ^-5 Aspheric surface 2 K -2.532097 A -0.743257 × 10 ^-3 B -0.108186 × 10 ^-3 C -0.441450 × 10 ^-6 D -0.136853 × 10 ^-5 Aspheric surface 3 K 104.679869 A -0.530692 × 10 ^-3 B 0.150688 × 10 ^-3 C -0.379387 × 10 ^-4 D 0.353657 × 10 ^-5 Aspheric surface 4 K -2.658845 A 0.466249 × 10 ^{-3 B 0.164076 × 10 -3 C -0.350780 ×} 10 -4 D 0.238071 × 10 -5 aspherical ^{5 K -830.367904 A 0.318361 × 10 -4} B -0.285290 × 10 -5 C 0.933920 × 10 -7 D -0.144591 × 10 - ⁸ Eccentricity (1) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 γ 0.00 Eccentricity (2) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 γ 0.00 Eccentricity (3) x 0.000 y 0.000 z 0.000 α 135.00 β 0.00 γ 0.00 Eccentricity (4) x 0.000 y 0.000 z 0.000 α -45.00 β 0.00 γ 0.00 Zoom interval Wide angle end Standard state Telephoto end d ₁ 8.89600 5.05300 1.55000 d ₂ 0.90000 1.86200 3.96300 d ₃ 1.00000 3.36400 5.28200 PX = 0.067860 PY = 0.068890 1 / | PX × d / n | = 0.828 1 / | PY × d / n | = 0.816 f ₁ / f _W = -1.423 | dz2 / dz1 | 0.417 13th surface | DY | = 0.128736 | Cxn (R) | = 1.089999 PXn / PX = 1.009124 PYn / PY = 0.514157 14th surface | DY | = 0.035813 | Cxn (R) | = 1.064767 PXn / PX = 0.610555 PYn / PY = 0.302037.

[0106] Example 2 Face Number of curvature radius interval eccentric refractive index Abbe number object surface ∞ 3000.0000 1 -14.5959 1.10 1.5842 30.5 (aspherical _{1) 2 8.5601 d 1 3 4.8421} 1.85 1.4924 57.6 ( aspherical ₂₎ 4 16.4615 d 2 5 -14.1016 3.18 1.4924 57.6 (Aspherical surface 3) 6 -4.9612 d ₃ (Aspherical surface 4) 7 ∞ 6.75 1.5254 55.8 8 ∞ -7.00 Eccentricity (1) 1.5254 55.8 (Dach surface) 9 ∞ -1.00 1.5254 55.8 10 ∞ 0.00 (Intermediate Image plane) 11 -18.9186 -13.00 1.5254 55.8 12 FFS [1] 6.50 Eccentricity (2) 1.5254 55.8 13 FFS [2] -10.00 Eccentricity (3) 1.5254 55.8 14 ∞ -1.00 15 66.3106 -2.00 1.4924 57.6 (Aspherical surface 5) 16 13.1300 -17.5 17 ∞ (eye _{point) FFS [1] C 5 3.4778} × 10 -3 C 7 6.0095 × 10 -3 C 8 -1.4317 × 10 -4 C 10 2.3364 × 10 -5 C 12 -1.2153 × 10 - ^{_{5 C 14 -4.1689 × 10 -5 C}} 16 -2.1124 × 10 -5 C 17 1.0067 × 10 -6 C 19 -1.3621 × 10 -7 C 21 2.1673 × 10 -7 FFS [2] C 5 -3.4583 × 10 - ^{_{3 C 7 -3.5731 × 10 -3 C}} 8 -7.2297 × 10 -5 C 10 3.7 _{^{91 × 10 -5 C 12 6.0444 ×}} 10 -6 C 14 1.7818 × 10 -5 C 16 1.2963 × 10 -5 C 17 2.1246 × 10 -7 C 19 -6.5748 × 10 -7 C 21 -2.8139 × 10 -7 non Spherical surface 1 K 0.0 A 0.556908 × 10 ^-3 B 0.114066 × 10 ^-4 C -0.816912 × 10 ^-6 D 0.127973 × 10 ^-7 Aspheric surface 2 K 0.0 A -0.785095 × 10 ^-3 B -0.220 860 × 10 ^-4 C 0.268203 × 10 ^-6 D 0.134583 × 10 ^-6 Aspheric surface 3 K 0.0 A -0.357489 × 10 ^-2 B -0.208213 × 10 ^-4 C -0.151639 × 10 ^-4 D 0.267806 × 10 ^-6 Aspheric surface 4 K 0.0 A -0.387927 × 10 ^-3 B -0.302023 × 10 ^-5 C -0.191371 × 10 ^-5 D 0.145761 × 10 ^-6 Aspherical surface 5 K 0.0 A -0.583779 × 10 ^-4 B 0.410445 × 10 ^-5 C -0.148461 × 10 ^-6 D 0.243011 × 10 ^-8 Eccentricity (1) x 0.000 y 0.000 z 0.000 α 36.00 β 0.00 γ 0.00 Eccentricity (2) x 0.000 y 0.000 z 0.000 α 24.00 β 0.00 γ 0.00 Eccentricity (3) x 0.000 y 0.000 z 0.000 α 30.00 β 0.00 γ 0.00 Zoom interval Wide-angle end Standard state Telephoto end d ₁ 9.80 200 4.22900 1.23600 d ₂ 4.65900 2.58400 1.20000 d ₃ 1.16000 5.28400 10.86300 PX = 0.0 61960 PY = 0.059958 1 / | PX × d / n | = 0.906 1 / | PY × d / n | = 0.937 f 1 / f W = -1.474 | dz2 / dz1 | = 0.404 fourteenth surface | DY | = 0.024412 | = 1.021539 PXn / PX = 0.591802 PYn / PY = 0.353921 15th surface | DY | = 0.028825 | Cxn (R) | = 0.944377 PXn / PX = 0.351871 PYn / PY = 0.351937.

[0107] Example 3 Face Number of curvature radius interval eccentric refractive index Abbe number object surface ∞ 3000.0000 1 -22.9639 1.18 1.5842 30.5 (aspherical _{1) 2 7.7308 d 1 3 4.5741} 1.85 1.4924 57.6 ( aspherical ₂₎ 4 9.3319 d 2 5 -80.4163 3.00 1.4924 57.6 (Aspheric surface 3) 6 -5.6384 d ₃ (Aspheric surface 4) 7 ∞ 6.75 1.5254 55.8 8 ∞ -7.00 Eccentricity (1) 1.5254 55.8 (Dach surface) 9 ∞ -1.00 1.5254 55.8 10 ∞ 0.00 (Intermediate Image plane) 11 -13.9385 -13.00 1.5254 55.8 12 FFS [1] 6.50 Eccentricity (2) 1.5254 55.8 13 FFS [2] -10.00 Eccentricity (3) 1.5254 55.8 14 15.0000 -17.5 15 ∞ (eye point) FFS [1] C ₅ 3.2245 × 10 ^-3 C ₇ 5.6946 × 10 ^-3 C ₈ -1.2355 × 10 ^-4 C ₁₀ 3.6247 × 10 ^-4 C ₁₂ -6.2895 × 10 ^-5 C ₁₄ -2.5262 × 10 ^-4 C ₁₆ -1.1383 × 10 ^-4 C ₁₇ -3.7563 × 10 ^-7 C ₁₉ -1.2527 × 10 ^-5 C ₂₁ -1.8527 × 10 ^-5 FFS [2] C ₅ -3.1288 × 10 ^-3 C ₇ -3.1342 × 10 ^-3 C ₈ -5.0518 × 10 ^-5 C ₁₀ 1.9094 × 10 ^-4 C ₁₂ -1.6951 × 10 ^-5 C ₁₄ -6.8459 × 10 ^-5 C ₁₆ -3.4335 × ^{_{10 -5 C 17 -1.8761 × 10 -6}} C 19 -8.4194 × 10 -6 C 21 -1.0520 × 10 -5 aspherical ^{1 K 0.0 A 0.492159 × 10 -3} B 0.417670 × 10 -5 C -0.540738 × 10 - ⁶ D 0.972913 × 10 ^-8 aspherical ^{2 K 0.0 A -0.659185 × 10 -3} B -0.932710 × 10 -4 C 0.124281 × 10 -4 D -0.631394 × 10 -6 aspherical 3 K 0.0 A -0.313312 × 10 ^{- 2} B -0.500276 × 10 ^-4 C -0.237804 × 10 ^-4 D 0.128760 × 10 ^-5 Aspheric surface 4 K 0.0 A -0.692339 × 10 ^-3 B -0.507237 × 10 ^-4 C -0.735594 × 10 ^-6 D 0.149800 × 10 ^-6 Eccentricity (1) x 0.000 y 0.000 z 0.000 α 36.00 β 0.00 γ 0.00 Eccentricity (2) x 0.000 y 0.000 z 0.000 α 24.00 β 0.00 γ 0.00 Eccentricity (3) x 0.000 y 0.000 z 0.000 α 30.00 β 0.00 γ 0.00 zoom interval angle end standard state telephoto end _{d 1 9.75900 4.30300 1.22500 d 2 3.72600} 2.33300 1.20000 d 3 1.16000 4.58500 9.67500 PX = 0.065880 PY = 0.063823 1 / | PX × d / n | = 0.785 1 / | PY × d / n | = 0.810 f ₁ / f _W = -1.587 | dz2 / dz1 | = 0.296 14th = DY | = 0.078247 | Cxn (R) | = 1.477586 PXn / PX = 0.527423 PYn / PY = 0.308272 15th surface | DY | = 0.026559 | Cxn (R) | = 0.837902 PXn / PX = 0.290284 PYn / PY = 0.299123 .

[0108] Example 4 Face Number of curvature radius interval eccentric refractive index Abbe number object surface ∞ 3000.0000 1 -19.9365 1.00 1.5842 30.5 2 8.2783 d 1 3 5.5701 2.29 1.5254 55.8 ( aspherical 1) 4 -7.2110 d ₂ (aspheric 2) 5 61.1432 1.00 1.5842 30.5 (Aspherical surface 3) 6 4.6565 d ₃ 7 7.4115 3.62 1.5254 55.8 (Aspherical surface 4) 8 ∞ -5.62 Eccentricity (1) 1.5254 55.8 9 ∞ 4.62 Eccentricity (2) 1.5254 55.8 10 ∞ 0.97 11 ∞ 0.00 ( Intermediate image plane) 12 9.8113 4.790 1.5254 55.8 13 FFS [1] -11.29 Eccentricity (3) 1.5254 55.8 14 FFS [2] 11.06 Eccentricity (4) 1.5254 55.8 15 -9.5324 18.50 (Aspherical surface 5) 16 ∞ (eye point) FFS [1] C ₅ 1.6846 × 10 ^-3 C ₇ 1.4460 × 10 ^-3 C ₈ -2.9162 × 10 ^-5 C ₁₀ 1.6492 × 10 ^-5 C ₁₂ -8.5798 × 10 ^-5 C ₁₄ -1.3999 × 10 ^-4 C ₁₆ -1.7154 × 10 ^-4 FFS [2] C ₅ 1.2605 × 10 ^-4 C ₇ 4.6400 × 10 ^-4 C ₈ -6.2667 × 10 ^-6 C ₁₀ -1.7665 × 10 ^-5 C ₁₂ -7.6269 × 10 ^-6 C ₁₄ -4.7899 × 10 ^-5 C ₁₆ -4.4251 × 10 ^-5 Aspheric surface 1 K -0.291996 A -0.8765 ^{25 × 10 -3 B -0.191271 × 10} -3 C 0.271519 × 10 -4 D -0.301278 × 10 -5 aspherical ^{2 K -2.767082 A -0.539385 × 10 -3} B -0.504533 × 10 -4 C 0.174462 × 10 - ⁶ D -0.104340 × 10 ^-5 Aspheric surface 3 K 566.690851 A 0.593883 × 10 ^-4 B -0.332514 × 10 ^-3 C 0.514749 × 10 ^-4 D -0.383078 × 10 ^-5 Aspheric surface 4 K -1.681157 A -0.225481 × 10 ^{-3 B 0.186321 × 10 -3 C -0.276166} × 10 -4 D 0.149906 × 10 -5 aspherical ^{5 K 1.224640 A 0.205896 × 10 -3} B 0.101282 × 10 -4 C -0.311554 × 10 -6 D 0.909549 × 10 - ⁸ Eccentricity (1) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 γ 0.00 Eccentricity (2) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 γ 0.00 Eccentricity (3) x 0.000 y 0.000 z 0.000 α 135.00 β 0.00 γ 0.00 Eccentricity (4) x 0.000 y 0.000 z 0.000 α -45.00 β 0.00 γ 0.00 zoom interval angle end standard state telephoto end _{d 1 8.62300 4.68200 1.56000 d 2 0.90000} 2.19700 4.52500 d 3 1.18500 2.09200 4.62300 PX = 0.057556 PY = 0.058623 1 / | PX × d / n | = 0.977 1 / | PY × d _{/N|=0.958 f 1 / f W = -1.376} | dz2 / dz1 | = 0.513 thirteenth surface | DY | = 0.007296 | Cxn ( R) | = 1.101680 PXn / PX = 0.153294 PYn / PY = 0.175340 fourteenth surface | DY | = 0.008421 | Cxn (R) | = 0.741144 PXn / PX = 0.049190 PYn / PY = 0.013120.

[0109] Example 5 Face Number of curvature radius interval eccentric refractive index Abbe number object surface ∞ 3000.0000 1 -15.2623 1.04 1.5842 30.5 2 7.7461 d 1 3 5.1541 2.00 1.5254 55.8 ( aspherical 1) 4 -6.9280 d ₂ (aspheric 2) 5 111.8332 1.37 1.5842 30.5 (Aspherical surface 3) 6 3.9482 d ₃ 7 6.0786 3.62 1.5254 55.8 (Aspherical surface 4) 8 -5.62 Eccentricity (1) 1.5254 55.8 9 ∞ 4.62 Eccentricity (2) 1.5254 55.8 10 ∞ 0.97 11 ∞ 0.00 ( Intermediate image plane) 12 8.4620 4.790 1.5254 55.8 13 FFS [1] -11.29 Eccentricity (3) 1.5254 55.8 14 FFS [2] 11.06 Eccentricity (4) 1.5254 55.8 15 ∞ 1.50 16 -11.3176 3.50 1.4924 57.6 (Aspherical surface 5) 17- 10.7190 18.5 18 ∞ (eye point) FFS [1] C ₅ 1.1019 × 10 ^-3 C ₇ 7.6491 × 10 ^-4 C ₈ 6.0323 × 10 ^-7 C ₁₀ 1.7840 × 10 ^-5 C ₁₂ -7.1728 × 10 ^-5 C ₁₄ -1.1838 × 10 ^-4 C ₁₆ -1.3183 × 10 ^-4 FFS [2] C ₅ -6.6090 × 10 ^-7 C ₇ 1.7793 × 10 ^-4 C ₈ -6.3307 × 10 ^-6 C ₁₀ -1.5820 × 10 ^-5 C ₁₂ -1.1137 × 10 ^-5 C ₁₄ -6.2245 × 10 ^-5 C ₁₆ -5.9291 × 1 0 ^-5 Aspheric surface 1 K -0.541122 A -0.108898 × 10 ^-2 B -0.117673 × 10 ^-3 C 0.144115 × 10 ^-4 D -0.350720 × 10 ^-5 Aspheric surface 2 K -2.314454 A -0.633399 × 10 ^-3 B 0.404467 × 10 ^-4 C -0.210454 × 10 ^-4 D -0.583491 × 10 ^-6 Aspheric surface 3 K 3339.433584 A 0.563862 × 10 ^-3 B -0.124243 × 10 ^-2 C 0.501009 × 10 ^-3 D -0.712596 × 10 ^-4 Aspheric surface 4 K -1.009764 A 0.664019 × 10 ^-3 B -0.141836 × 10 ^-3 C 0.365377 × 10 ^-4 D -0.339630 × 10 ^-5 Aspheric surface 5 K -0.449478 × 10 ¹⁵ A -0.569097 × 10 ^-4 B- 0.488156 × 10 ^-6 C -0.434723 × 10 ^-7 D 0.147301 × 10 ^-8 Eccentricity (1) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 γ 0.00 Eccentricity (2) x 0.000 y 0.000 z 0.000 α 0.00 β 45.00 gamma 0.00 eccentric (3) x 0.000 y 0.000 z 0.000 α 135.00 β 0.00 γ 0.00 eccentricity (4) x 0.000 y 0.000 z 0.000 α -45.00 β 0.00 γ 0.00 zoom interval angle end standard state telephoto end d ₁ 7.95900 4.36800 1.50000 d ₂ 0.90000 2.27800 4.89800 d ₃ 1.74000 2.15300 4.13900 PX = 0.046826 PY = 0.047385 1 / | PX × d / n | = 1.200 1 / | PY × d / n | = 1.186 f ₁ / f _W = -1.121 | dz2 / dz1 | = 0.618 thirteenth surface | DY | = 0.007133 | Cxn (R = 1.393134 PXn / PX = 0.099672 PYn / PY = 0.141891 14th surface | DY | = 0.005648 | Cxn (R) | = 2.330055 PXn / PX = 0.023185 PYn / PY = 0.000085

Next, the wide-angle end, the standard state,
FIGS. 9 to 11 show the lateral aberration states at the telephoto end center and the maximum angle of view in the X and Y directions, respectively. In the figures showing these lateral aberrations, the numbers shown in parentheses are (horizontal (X
Direction), the vertical (Y direction) angle of view, and a lateral aberration diagram at the angle of view. However, these lateral aberrations are lateral aberrations on an image forming plane where an aberration-free imaging lens is arranged on the observation side of the eyepiece optical system Oc.

The real image type finder optical system of the present invention can be used for a finder optical system 13 of an electronic camera as shown in FIG. 12, for example. In FIG. 12, (a)
Is a perspective view of the electronic camera as viewed from the front side, (b) is a perspective view of the electronic camera as viewed from the rear side, (c) is an optical path diagram showing an optical system of the electronic camera, 1, a finder optical system 13 having a finder optical path 14, a shutter 15, a flash 16, a liquid crystal display monitor 17, and the like. The finder optical system 13 includes, for example, an objective optical system as shown in FIG. The system comprises a system Ob, an image reversing optical system PP, and an eyepiece optical system Oc, and is of a type that allows a visual field to be viewed directly. Note that a transparent finder window cover 21 is disposed on the incident side of the objective optical system Ob of the finder optical system 13.

The photographing optical system 11 includes a photographing objective optical system 18 and a filter 19 such as an infrared cut filter.
And an electronic image pickup device 20 arranged on the image forming plane of the photographing objective optical system 18. A subject image picked up by the electronic image pickup device 20 or an image recorded in a recording device is displayed on the liquid crystal display monitor 17. Is done.

As a matter of course, the real image type finder optical system according to the present invention is used for the finder optical system of a compact photographic camera for photographing a subject image by arranging a photographic film in place of the electronic image pickup device 20. Can be.

The above-described real image type viewfinder optical system of the present invention and an apparatus using the same can be constructed, for example, as follows. [1] A finder objective optical system, an image inverting optical system for turning an object image formed by the finder objective optical system into an erect image, and an eyepiece optical system, wherein the eyepiece optical system is separated from the photographing optical path. In a real image type finder optical system that forms an optical path, the finder objective optical system has a plurality of lens groups, and changes the group interval between the plurality of lens groups when zooming from a wide-angle end to a telephoto end. Wherein the image inversion optical system has a plurality of reflecting surfaces, and among the plurality of reflecting surfaces, the shape of at least one reflecting surface disposed closer to the eyepiece optical system than the object image is a light beam. The image inverting optical system is formed of a curved reflecting surface that gives power, and the image inverting optical system includes a rotationally asymmetric surface that corrects rotationally asymmetric decentering aberration generated by the curved reflecting surface. Image finder optical system.

[2] A finder objective optical system, an image reversing optical system for converting an object image formed by the finder objective optical system into an erect image, and an eyepiece optical system are provided, which are separated from the photographing optical path. In a real image type finder optical system that forms a finder optical path, the image inversion optical system has a plurality of reflection surfaces, and among the plurality of reflection surfaces,
At least one reflecting surface located closer to the eyepiece optical system than the object image is formed by a curved reflecting surface that gives power to a light beam, and the image inverting optical system is generated by the curved reflecting surface. A rotationally asymmetric surface for correcting rotationally asymmetric eccentric aberration is provided, and the following condition (3-
A real image type finder optical system, which satisfies 1) and (3-2). 0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) However, the center or aperture of the objective optical system passes through the object point center. A ray that passes through the center to reach the center of the intermediate image plane, passes through the eyepiece optical system, and enters the center of the pupil is defined as an axial principal ray, and is defined by a straight line until the axial ray intersects the rotationally asymmetric surface. The axis is the Z axis, and is orthogonal to the Z axis, and
When an axis in the eccentric plane of the rotationally asymmetric surface is defined as a Y axis, and an axis orthogonal to the Z axis and an axis orthogonal to the Y axis is defined as an X axis, PXn and PYn each have a reflecting surface having power. The power of the surface in the X and Y directions near the axial principal ray of
PX and PY pass parallel rays of a small height Δ in the X and Y directions along the axial principal ray from the intermediate image toward the observer side, and the rays are transmitted to the observer side. This is a value obtained by dividing the sine of the inclination angle with respect to the axial principal ray emitted from the nearest plane by the above Δ, and is a value defined as the power in the X and Y directions of the entire eyepiece optical system.

[3] In the above item 1, the following condition (3)
(1) A real image type finder optical system satisfying (3-2). 0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) However, the center or aperture of the objective optical system passes through the object point center. A ray that passes through the center to reach the center of the intermediate image plane, passes through the eyepiece optical system, and enters the center of the pupil is defined as an axial principal ray, and is defined by a straight line until the axial ray intersects the rotationally asymmetric surface. The axis is the Z axis, and is orthogonal to the Z axis, and
When an axis in the eccentric plane of the rotationally asymmetric surface is defined as a Y axis, and an axis orthogonal to the Z axis and an axis orthogonal to the Y axis is defined as an X axis, PXn and PYn each have a reflecting surface having power. The power of the surface in the X and Y directions near the axial principal ray of
PX and PY pass parallel rays of a small height Δ in the X and Y directions along the axial principal ray from the intermediate image toward the observer side, and the rays are transmitted to the observer side. This is a value obtained by dividing the sine of the inclination angle with respect to the axial principal ray emitted from the nearest plane by the above Δ, and is a value defined as the power in the X and Y directions of the entire eyepiece optical system.

[4] The real image type viewfinder optical system according to any one of the above items 1 to 3, wherein the rotationally asymmetric surface is disposed closer to the eyepiece optical system than the object image.

[5] The real image finder optical system according to any one of the above items 1 to 3, wherein the rotationally asymmetric surface is formed on a reflection surface of the image inversion optical system.

[6] The real-image finder optical system according to any one of the above items 1 to 3, wherein the rotationally asymmetric surface is formed on the curved reflecting surface.

[7] The real image finder optical system according to any one of the above items 1 to 6, wherein a plurality of the rotationally asymmetric surfaces are arranged in the image reflecting optical system.

[8] The real image type viewfinder optical system according to any one of the above items 1 to 7, wherein the image inverting optical system and the eyepiece optical system are integrated.

[0122]

[9] The real image type finder optical system according to any one of the above items 1 to 8, wherein the following conditional expressions (4-1) and (4-2) are satisfied. 0.1 <1 / | PX × d / n | <1 (4-1) 0.1 <1 / | PY × d / n | <1 (4-2) A ray that passes through the center, passes through the center of the aperture or the center of the aperture of the objective optical system, reaches the center of the intermediate image plane, and further passes through the eyepiece optical system and enters the center of the pupil is defined as an axial principal ray. An axis defined by a straight line that intersects the asymmetric surface is defined as a Z-axis, orthogonal to the Z-axis, and
When the axis in the eccentric plane of the rotationally asymmetric surface is defined as the Y axis, and the axis orthogonal to the Z axis and the axis orthogonal to the Y axis is the X axis, PX and PY are closer to the observer side than the intermediate image. When a parallel ray having a minute height Δ is passed in the X direction and the Y direction along the axial principal ray toward the optical axis, the ray exits from the plane closest to the observer side. Tilt angle with respect to
n is a value defined by the power of the entire eyepiece optical system in the X and Y directions, and d is a value obtained when the image reversing optical system closer to the observer than the intermediate image is developed. The length of the axial principal ray, n, is the refractive index of the image reversing optical system closer to the observer than the intermediate image.

[10] A real image type finder optical system characterized by satisfying the following conditional expressions (5-1) and (5-2) in any one of the above items 1 to 9. 0.03 <PX <0.5 (5-1) 0.03 <PY <0.5 (5-2) However, it passes through the center of the object point, and the center of the aperture of the objective optical system or the aperture. A ray that passes through the center to reach the center of the intermediate image plane, passes through the eyepiece optical system, and enters the center of the pupil is defined as an axial principal ray, and is defined by a straight line until the axial ray intersects the rotationally asymmetric surface. The axis is the Z axis, and is orthogonal to the Z axis, and
When the axis in the eccentric plane of the rotationally asymmetric surface is defined as the Y axis, and the axis orthogonal to the Z axis and the axis orthogonal to the Y axis is the X axis, PX and PY are closer to the observer side than the intermediate image. When a parallel ray having a minute height Δ is passed in the X direction and the Y direction along the axial principal ray toward the optical axis, the ray exits from the plane closest to the observer side. Tilt angle with respect to
This is a value obtained by dividing n by the above Δ, and is defined as the power in the X and Y directions of the entire eyepiece optical system.

[11] The real image type finder optical system according to any one of the above items 1 to 10, which satisfies the following conditional expression (1-1). | DY | <0.5 (1-1) However, it passes through the center of the object point, passes through the center of the aperture or the center of the aperture of the objective optical system, reaches the center of the intermediate image plane, and further passes through the eyepiece optical system. The ray incident on the center of the pupil is the axial principal ray, the axis defined by the straight line until the axial ray intersects the rotationally asymmetric surface is the Z axis, and is orthogonal to the Z axis, and
When the axis in the eccentric plane of the rotationally asymmetric surface is defined as the Y axis, and the axis orthogonal to the Z axis and the axis orthogonal to the Y axis is the X axis, when the objective optical system is a single focus lens, In that state, in the case of a zoom lens, the value of tan of the normal to the rotationally asymmetric surface at the point where the principal ray of the maximum angle of view in the X direction intersects with the rotationally asymmetric surface in the YZ plane at the wide angle end; The difference between the point at which the axial chief ray intersects the rotationally asymmetric surface and the value of tan of the normal to the rotationally asymmetric surface is defined as DY.

[12] In any one of the aforementioned items 1 to 11, the rotationally asymmetric surface may be formed so as to satisfy one of the following conditions (2-1) and (2-2). Features a real image finder optical system. | Cxn (R) | <1 (2-1) or 1 <| Cxn (R) | <10 (2-2) However, the center of the object point passes through the center of the stop of the objective optical system. Alternatively, a ray reaching the center of the intermediate image plane through the center of the aperture and further entering the pupil center through the eyepiece optical system is defined as an axial chief ray, and is defined by a straight line until the axial ray intersects the rotationally asymmetric surface. The axis to be set is the Z axis, and is orthogonal to the Z axis, and
When the axis in the eccentric plane of the rotationally asymmetric surface is defined as the Y axis, and the axis orthogonal to the Z axis and the axis orthogonal to the Y axis is the X axis, when the objective optical system is a single focus lens, In this state, in the case of a zoom lens, the curvature in the X direction of the portion where the principal ray of the maximum angle of view in the Y positive direction at the wide angle end and the principal ray of the maximum angle of view in the negative Y direction at the wide angle end hits the surface Is Cxn (R).

[13] In any one of the above items 1 to 12, the finder objective optical system includes a negative first lens group and a positive second lens group in order from the object side.
A real image type viewfinder optical system, wherein a group distance between the first lens group and the second lens group is reduced at the time of zooming from a wide angle end to a telephoto end.

[14] The real image type finder optical system according to the above item 13, wherein the finder objective optical system satisfies the following condition (6-1). -4.0 <f ₁ / f _W <0 (6-1) where f ₁ is the focal length of the first lens unit, and f _W is the focal point of the entire finder objective optical system at the wide-angle end. Distance.

[15] In any one of the above items 1 to 12, the finder objective optical system may include, in order from the object side, a negative first lens group, a positive second lens group, and a positive third lens group. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced, and the distance between the second lens group and the third lens group is reduced. A real image type viewfinder optical system characterized by being configured to change.

[16] The real image type finder optical system according to the above item 13, wherein the finder objective optical system satisfies the following condition (6-2). 0 <| dz2 / dz1 | <2.0 (6-2) where dz1 is the amount of change in the group interval from the wide-angle end to the telephoto end of the first lens unit and the second lens unit, and dz2 is the second. This is the amount of change in group interval between the wide-angle end and the telephoto end of the lens group and the third lens group.

[17] The real-image finder optical system according to the above item 15 or 16, wherein the third lens group is moved on the optical axis when zooming from the wide-angle end to the telephoto end. system.

[18] In any one of the above items 13 to 17, the second lens group is configured to move on the optical axis when zooming from the wide-angle end to the telephoto end. Real image finder optical system.

[19] In any one of the above items 13 to 18, the first lens group is configured to move on the optical axis when zooming from the wide-angle end to the telephoto end. Real image finder optical system.

[20] In any one of the above items 1 to 19, the image inverting optical system may be a medium in which a refractive index (n) including a reflecting surface is larger than 1.3 (n> 1.3). A real image type finder optical system comprising two prism members formed by the above-described method.

[21] The real-image finder optical system according to the above item 20, wherein an intermediate image is formed between the two prism members by the finder objective optical system.

[22] In the above item 21, the rotationally asymmetric surface and the curved reflecting surface are disposed on a prism member disposed closer to an observer's eye than the object image among the two prism members. A real image type finder optical system characterized by the following.

[23] The real-image finder optical system according to any one of the above items 1 to 22, wherein the rotationally asymmetric surface is formed by a rotationally asymmetric surface having only one symmetric surface.

[24] In the above item 23, when the rotationally asymmetric surface has the optical axis as the Z axis, the X axis perpendicular to the Z axis
A real image type finder optical system, wherein only one symmetrical surface is formed along one of the axis and the Y axis.

[25] In any one of the aforementioned items 1 to 24, the real image type finder optical system is formed by the photographing objective optical system and the photographing objective optical system arranged on the photographing optical path. A camera device comprising: a photographing optical system having an image pickup device for picking up an object image.

[26] The electronic camera device according to the above item 25, wherein the image pickup device comprises an electronic image pickup device.

[0140]

As is apparent from the above description, according to the present invention, the focal length of the eyepiece optical system can be reduced by giving power to the reflection surface of the image inverting optical system closer to the observer than the intermediate image. Thus, it is possible to obtain a real image type finder capable of observing a large image. At the same time, it is possible to obtain a real image finder with reduced chromatic aberration.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view at a wide-angle end of a real image type finder according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating positions of respective groups at a wide-angle end (a), a standard state (b), and a telephoto end (c) of the objective optical system according to the first embodiment.

FIG. 3 is a cross-sectional view of a real image type viewfinder of Example 2 of the present invention at a wide angle end (a), in a standard state (b), and at a telephoto end (c).

FIG. 4 is a sectional view of a real image type viewfinder according to a third embodiment of the present invention at a wide angle end (a), in a standard state (b), and at a telephoto end (c).

FIG. 5 is a cross-sectional view at a wide angle end of a real image type finder according to a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating positions of respective groups at a wide-angle end (a), a standard state (b), and a telephoto end (c) of the objective optical system according to the fourth embodiment.

FIG. 7 is a cross-sectional view at a wide-angle end of a real image type finder according to a fifth embodiment of the present invention.

FIG. 8 is a diagram illustrating positions of respective groups of the objective optical system of Example 5 at a wide angle end (a), a standard state (b), and a telephoto end (c).

FIG. 9 is an aberration diagram showing a lateral aberration state at a wide-angle end in Example 1.

FIG. 10 is an aberration diagram showing a lateral aberration state in the standard state of Example 1.

11 is an aberration diagram showing a lateral aberration state at a telephoto end in Example 1. FIG.

FIG. 12 is a diagram for explaining an electronic camera provided with the real image type viewfinder optical system of the present invention.

FIG. 13 is a conceptual diagram for explaining field curvature generated by an eccentric reflecting surface.

FIG. 14 is a conceptual diagram for describing astigmatism generated by a decentered reflecting surface.

FIG. 15 is a conceptual diagram for explaining coma generated by a decentered reflecting surface.

FIG. 16 is a diagram for explaining a parameter DY used in the present invention.

[Explanation of symbols]

Ob: Objective optical system PP: Image reversal optical system Oc: Eyepiece optical system G1: First lens group G2: Second lens group G3: Third lens group P1, P2: Prism block P3: Dach prism P4: Penta prism S _1- S ₁₈ optical surface (including intermediate image plane and eye point) M concave mirror 11 photographing optical system 12 photographing optical path 13 finder optical system 14 finder optical path 15 shutter 16 flash 17 liquid crystal display monitor 18 ... Objective optical system for photographing 19 ... Filter 20 ... Electronic imaging device 21 ... Finder window cover

Claims (3)

[Claims] An objective optical system for a finder, an image inverting optical system for converting an object image formed by the objective optical system for a finder into an erect image, and an eyepiece optical system are separated from an optical path for photographing. In a real image type finder optical system that forms an optical path for a finder, the objective optical system for a finder has a plurality of lens groups, and changes a group interval between the plurality of lens groups when zooming from a wide-angle end to a telephoto end. Wherein the image inverting optical system has a plurality of reflecting surfaces, and among the plurality of reflecting surfaces, a shape of at least one reflecting surface disposed closer to the eyepiece optical system than the object image is. The image inverting optical system is formed of a curved reflecting surface that gives power to the light beam, and the image inverting optical system includes a rotationally asymmetric surface that corrects rotationally asymmetric decentering aberration generated by the curved reflecting surface. Real-image viewfinder optical system. 2. An objective optical system for a finder, an image inverting optical system for turning an object image formed by the finder objective optical system into an erect image, and an eyepiece optical system, which is separated from a photographing optical path. In a real image type finder optical system that forms an optical path for a finder, the image inversion optical system has a plurality of reflection surfaces, and among the plurality of reflection surfaces, at least one disposed closer to the eyepiece optical system than the object image. The shape of one reflecting surface is formed by a curved reflecting surface that gives power to a light beam, and the image inverting optical system includes a rotationally asymmetric surface that corrects rotationally asymmetric eccentric aberration generated by the curved reflecting surface. And a real-image finder optical system satisfying the following conditions (3-1) and (3-2). 0 <| PXn / PX | <5 (3-1) 0 <| PYn / PY | <5 (3-2) However, the center or aperture of the objective optical system passes through the object point center. A ray that passes through the center to reach the center of the intermediate image plane, passes through the eyepiece optical system, and enters the center of the pupil is defined as an axial principal ray, and is defined by a straight line until the axial ray intersects the rotationally asymmetric surface. The axis is the Z axis, and is orthogonal to the Z axis, and
When an axis in the eccentric plane of the rotationally asymmetric surface is defined as a Y axis, and an axis orthogonal to the Z axis and an axis orthogonal to the Y axis is defined as an X axis, PXn and PYn each have a reflecting surface having power. The power of the surface in the X and Y directions near the axial principal ray of
PX and PY pass parallel rays of a small height Δ in the X and Y directions along the axial principal ray from the intermediate image toward the observer side, and the rays are transmitted to the observer side. This is a value obtained by dividing the sine of the inclination angle with respect to the axial principal ray emitted from the nearest plane by the above Δ, and is a value defined as the power in the X and Y directions of the entire eyepiece optical system. 3. The real image type finder optical system according to claim 1, wherein the image inverting optical system and the eyepiece optical system are integrated.